Something really strange happens when a cane frog sits down to eat : ScienceAlert
Contrary to popular belief, it is not possible to swallow your own tongue. At least if you’re human. It turns out that toads do this on purpose every time they eat.
“We know a lot about how frogs extend their tongues and how they stick to their prey, but before this study, basically everything that happens after they close their mouths was a mystery,” says University of Florida herpetologist Rachel Keeffe.
So Keeffe and colleagues used high-speed X-rays to understand what was happening when these amphibians closed their mouths around a meal, and the results were completely unexpected.
“We weren’t sure what was going on at first,” says Keeffe. “The whole lower part of the mouth is drawn back into the throat and the tongue with it.”
Frogs are known for catching their prey quick, sticky tonguesbut therein lies the problem that their unusual anatomy had to solve: how then to extract food from that sticky whip and send it down the intestines.
From capture to ingestion, the entire process takes less than two seconds, but there is a whole series of events that take place inside the frog during this short period of time.
The team attached tiny metal beads to the frog’s tongue so they could track muscle movements on X-rays. As shown in the video below, the orange marker on the tip of its tongue flicks to capture the insect and then returns to the frog’s mouth. But it doesn’t stop there, continuing down the throat a full 4.5 centimeters (1.8 inches), until it almost touches the frog’s heart.
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“The mean distance the tongue stretches during retraction equals or exceeds the mean distance it stretches during protrusion,” researchers to write in their paper, explaining that the maximum protrusion of the tongue averaged 4.1 centimeters.
Here near their heart, hyoid – a flexible cartilage plate suspended by strings of muscles – clicks against the tongue.
“The hyoid protrudes and presses the tongue against the roof of the mouth, whereupon it moves forward, essentially scraping the food into the esophagus,” explains Keeffe.
Hyoid (which is also in some toads use to call by clicking) naturally closes the floor of the mouth while the toad rests. But its connection to the tongue means that it opens as the muscle expands, opening wide as the frog opens its mouth, ready for the tongue to return.
This is probably why frogs and many frogs have strange ridges or ‘teeth’ like bumps on the roof of their mouths, Keeffe and team suspect; to help destick this food. Hyoid markers precisely hit this area in the researchers’ 3D reconstruction. The flexibility of the hyoid would also aid in the scraping task.
“Even if the frog moves the tongue into the mouth during a double swallow, the prey remains attached to the tongue during the manipulation,” Keeffe and colleagues to write. This suggests that frogs require a hyoid mechanism to successfully expel food.
The researchers now want to replicate these studies to see if this mechanism of tongue retraction and scraping is universal across the board almost 5,000 species of frogsamong which there is an enormous variety of hyoid and tongue forms.
This research was published in Organismal Biology.
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